Several agents were found to stimulate normal macrophages to exert a tumoricidal effect (BM 12, 531, Bru Pel, MVE, glucan and thymopoeiten fractions. Tumor metastases and growth was retarded by MVE, Bru Pel and Interferon. Prostaglandins and dibutyryl cyclic AMP exhibit an inhibitory action on stimulation of macrophage tumoricidal activity. Corticosteroid hormones also exert an inhibitory action on macrophage activity. Lymphokine contains a macrophage activating factor not neutralizable by anti-Interferon antibody. Adriamycin, cytoxan and 5-fluorouracil stimulate macrophage tumoricidal activity while depressing T and B cells. Human macrophages demonstrate enhanced tumoricidal activity after exposure to Interferon, MVE and Bru Pel. MVE, Interferon, and Bru Pel when used in combination with chemotherapy retarded tumor growth and increased survival in the leukemia and mammary carcinoma tumor models. MVE analogs, Bru Pel and glucan potentiate tumor cell vaccines.